1. Field of the Invention
The present invention relates to an analog digital converter, a signal processing system using the same, and an imaging device, and particularly to an analog digital converter, a signal processing system using the same, and an imaging device, mounted on a system LSI (Large Scale Integration) or the like.
2. Description of the Related Art
In recent years, system LSIs have come to be mounted on mobile devices such as digital still cameras and so forth. With the system LSI, a device is designed using multiple single-function LSIs. This enables simple wiring, as well as reduced area of LSIs. Thus, the system LSI has the advantage of allowing the user to design a device with a small size.
A system of a digital CCD camera is disclosed in Patent document 1.
[Patent Document 1]
Japanese Patent Application Laid-open No. 2001-78088
A system disclosed in Patent Document 1 and shown in FIG. 1 thereof includes an AD (Analog Digital) converter 3. The AD converter 3 is formed with a fixed specification. Accordingly, with a system which requires 8-bit precision in normal operation, but requires 10-bit precision in special operation, such a system requires an AD converter with a 10-bit specification.
An AD converter with a 10-bit specification leads to larger power consumption than that of an AD converter with an 8-bit specification due to difference in power consumption between 8-bit operation and 10-bit operation. Accordingly, the AD converter of a system, which requires high-precision signal processing in special operation, leads to excessive power consumption in normal operation.